Monday, February 20, 2012

Thoughts on underground storage

20 Feb 2012: Thoughts on commercialising domestic solar earth charging
   As you can read from this blog, this house is already well better than carbon zero, and the feed in tariff gives me zero energy bills for the next 23 years. So you could say to that, that I don't actually 'need' to do this proposed work with the Kingspan tubes.

However, this is research and development… thinking about the future… 
   My hunch is that potential customers would not want the burden of a large hand built 3 cubic meter sun box on their wall. They might be more easily persuaded if a neat 2 or 4 sqm of evacuated tubes would do it just as well, especially if it can be installed in just a couple of days, as an economical add-on to a GSHP installation.  We need a couple of summers and winters with these installed to find out for real (I know that it can be computer modelled, but is this really proof?). If we are to have a display at Ecobuild in a few years time, the Tubes method would look more convincing. Kingspan Renewables have a stand at the coming event in March 2012, and I would like this to appear one day.

Borehole thoughts
If there is ever any hope of solar charging, the first decision is to have a borehole, not a horizontal loop. There are abundant reasons why a borehole is better than a horizontal, even if we do not consider charging - if a customer has enough land to park a horse on, e.g. a paddock, then do horizontal. But for most urban dwellers, the vertical option avoids the risks associated with undersized horizontal loops. It is quick to drill, minimal spoil, is unaffected by seasons and it can be thermally recharged.
   What happens if it is the wrong sort of ground? As it is expensive to do a pre-drilling ground check, I would advocate that GSHP customers always tell their borehole drillers to drill the full depth required for a GSHP assuming that solar charging would not be fitted. This is the safe route, in case solar charging pump or panels ceased to work. It would be unwise to undersize the boreholes based on hope. I would advocate that they consider the option of a cluster of shallower holes, reducing the risk of hitting a bad layer, e.g. limestone caverns.
  THEN! if the drillers report that the soil has been good almost all the way down, the solar charging is an easy retrofit. Prior to this, one can consider the building design and identify the suitable location for the solar collector, and a suitable route for piping, and a location for thermostat, energy meter and pump. Then have the drilling done and hope that the soil is good enough for solar energy charging. If it is not, e.g., it has water bearing gravel layers, it does not need solar charging as the water will provide the required heat.

PS, writing this, i am (typically) procrastinating. I am meant to be doing a lecture on thermal storage for next friday, and I seem to be spending far too long on updating this blog!

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